# User talk:Gaaijz

## welcome!

Welcome to Rosetta Code! If you have any questions, drop them in the appropriate talk page, and someone will get back to you. If you have a more general question, try Mwn3d's or my talk pages. --Short Circuit 04:10, 2 September 2008 (UTC)

## Jers

Hey Arie. This is Dan Bron from the J forums. Tracy Harms is here too. It's good to have J representation on RosettaCode. I'm glad you posted a J solution to the Pyramid of Numbers, that was near the top of my to do list. Have you considered posting a task along the lines of your Rabbit Sequence?

Oh, by the way, I linkified your user page. I hope you don't mind. Go ahead and revert it if you like it better the other way.

DanBron 13:48, 2 September 2008 (UTC)

## Zigzag

```zigzag m n = take m .transp_wof \$ zipWith id (cycle [reverse,id]) antiDiags where
mmn        = min m n
antiDiags  = unfoldr (\((c:cs),xs) -> if null xs then Nothing else Just (take c xs,(cs,drop c xs)))
([1..mmn-1]++(replicate (succ.abs \$ m-n) mmn)++[mmn-1,mmn-2..0], [0..m*n-1])
transp_wof = unfoldr (\xs -> if null xs then Nothing else Just \$ next xs)
next xs    =  (,) (concatMap (take 1) ks) ((map (drop 1) \$ drop 1 ks) ++ ts)
where (ks,ts) = splitAt n xs

```
Slower version, almost complete emulation of the J-solution
```groupon f x y= f x == f y
tab n = fst . until (null.snd) (\(xs,ys)-> (xs++[take n ys], drop n ys)) . (,) []
grade xs = map snd. sort \$ zip xs [0..]

zigzagJ m n = tab n. grade .concat \$ zipWith id (cycle [reverse,id]) fdiag
where fdiag = map (map snd). groupBy (groupon fst).sortBy (comparing fst)
\$ zip (map sum \$ sequence [[0..m-1],[0..n-1]] ) [0..]
```
```*Main> sum.map sum \$ zigzag  500 500
1185103928
(0.69 secs, 103908376 bytes)

*Main> sum.map sum \$ zigzagJ 500 500
31249875000
(4.55 secs, 575802084 bytes)
```

## Generic swap

Hello again. I've responded to your question re: Generic swap.

--DanBron 16:05, 29 September 2008 (UTC)